Expansion gap compensating system for a die

ABSTRACT

An expansion gap compensating system for a die that is especially useful in the area of high-temperature diecasting, e.g., at temperatures of about 1,300* F. and up. When a die&#39;&#39;s impression block is fabricated of a metal having a different expansion coefficient than that of the die&#39;&#39;s holding block crevasses or expansion gaps tend to open between the two blocks upon heating of the die assembly to high temperature from room temperature. The width of these expansion gaps may vary from thousandths of an inch to hundredths of an inch or more, and is mainly dependent on the difference in expansion coefficients of the block metals and on the casting or operating temperature. The system of this invention permits an impression block and a holding block fabricated of, for example, a refractory metal and a steel respectively, (a) to be simply and easily assembled and maintained together as a die in tight and safe operating relation without damage to either, and (b) to be maintained in an exact centered or preset position relative one to another, at all times throughout a casting run. Thus, the expansion gap compensating system acts to compensate for expansion gaps that tend to open between related impression and holding blocks as the die assembly is heated up to and operated at high temperatures, as well as to compensate for the contracting of those gaps as the die assembly cools after the casting run.

United States Patent [72] Inventor Joseph A. WolteringContinuation'in-part of application Ser. No. 737,480, June 17, 1968, nowabandoned.

[54] EXPANSION GAP COMPENSATING SYSTEM FOR A DIE 23 Claims, 8 DrawingFigs.

[52] US. Cl 164/137, 18/44, 164/303, 164/342, 249/82 [51] Int. Cl 822d17/24, B29c 1 1/00 [50] Field of Search 164/47,

113, 137, 303-305, 339343; 18/35, 38, 42-44, (Digest 29); 249/80, 82,165, 166; 29/405 FORElGN PATENTS 186,785 9/1956 Austria 164/3421,316,838 12/1962 France 164/342 Primary Examiner-Robert D. BaldwinAttorney-Wood, Herron & Evans ABSTRACT: An expansion gap compensatingsystem for a die that is especially useful in the area ofhigh-temperature diecasting, e.g., at temperatures of about 1,300 F. andup. When a dies impression block is fabricated of a metal having adifferent expansion coefficient than that of the dies holding blockcrevasses or expansion gaps tend to open between the two blocks uponheating of the die assembly to high temperature from room temperature.The width of these expansion gaps may vary from thousandths of an inchto hundredths of an inch or more, and is mainly dependent on thedifference in expansion coefficients of the block metals and on thecasting or operating temperature. The system of this invention permitsan impression block and a holding block fabricated of, for example, arefractory metal and a steel respectively, (a) to be simply and easilyassembled and maintained together as a die in tight and safe operatingrelation without damage to either, and (b) to be maintained in an exactcentered or preset position relative one to another, at all timesthroughout a casting run. Thus, the expansion gap compensating systemacts to compensate for expansion gaps that tend to open between relatedimpression and holding blocks as the dieassembly is heated up to andoperated at high temperatures, as well as to compensate for thecontracting of those gaps as the die assembly cools after the castingrun.

PATENTEU JUN 1 I97! SHEET 2 OF 3 PATENTEU JUN Hen SHEET 3 or 3 rEXPANSION GAP COMPENSATING SYSTEM FOR A DIE This application is acontinuation-in-part application of U.S. Ser. No. 737,480, filed June17, 1968, now abandoned.

This invention relates to dies and, more particularly, relates to anexpansion gap compensating system that is especially advantageous fordies used when casting high melting point materials.

Diecasting is a well-known method of forming cast metal parts; itbasically involves injecting a molten metal charge under pressure into adie cavity. The basic components of a diecasting-type machine are a dieassembly of two halves or dies that together define a negativeimpression or cavity of the object that is desired, a chamber forholding a charge of molten metal, and a plunger for transferring themetal charge under pressure from the chamber to the die, The basicfunctions of such a machine are to close and hold the two halves or diesof the die assembly tightly together for establishing the die cavity; toinject the molten metal under pressure into the die cavity; and then toopen the die assembly and eject the finished casting from the cavity.

The die assembly for diecasting-type machines basically consists of twoseparate halves or dies, each containing a part of the castingimpression, plus cores if needed for the part to be cast. The die halvesare mounted on the diecasting machine and are so arranged that one isstationary (called the cover die) while the other is movable (called theejector die). The

mating surface or front face of each die is finished so that the diesfit snugly together at an interface to form the die cavity when in theclosed position. When the machine is closed the two halves of the dieassembly are locked tightly together in precise register, after whichthe molten metal is injected from the injection apparatus under pressureinto the die cavity so formed through a gate in the assembly.Subsequently, the two die halves are drawn apart to allow ejection ofthe casting. Proper means for rapidly ejecting the casting from the dieas" sembly is provided in the form of ejector pins mounted to an ejectorplate reciprocably assembled with the ejector die. Thus, the movable orejector die usually contains, in addition to a portion of the castingimpression, movable elements such as cores, slides, and ejectormechanism.

The material from which the die cavity is formed is one factor indetermining the commercial success of the diecasting process. Dies are,of necessity, expensive and the money expended in fabricating them mustbe justified by good service life as measured by number of castingsproduced. Since the molten metal is forced into the die cavity underpressure the die must be capable of withstanding impact and mechanicalshock, and because the metal is molten and at a relatively hightemperature the die must be capable of withstanding thermal shock aswell. Also, and very importantly, the die must be able to resist washingor erosion of the cavity configuration by the metal being cast. Thecombination of these three factors, plus others, means that the diecavity must be constructed of very good quality steels. With the lowermelting point alloys used in diecasting, for example, tin, lead, andzinc, the problem of securing a long life for the die at an economicalper casting cost is not so acute. However, with the higher melting pointalloys, for example, magnesium, aluminum, gray iron, and copper-zincalloys, the die steel must be of the best possible grade tool steel andmust be produced to quite rigid specifications to overcome, inparticular, the cavity erosion or wash problem.

With the casting of such high melting point metals as are presently usedin the diecasting industry, for example, the magnesium, aluminum, grayiron, and copper-zinc alloys, and with diecasting technology rapidlyapproaching that point where even higher melting point metals will bediecast, the problems of eroding and washing of the die cavityconfiguration and thermal shock to the die are particularly acutebecause of those metals high melting points. ln an effort to combat thisproblem there has been developed a structural die design which comprisesa separate impression block for each of the ejector and cover diehalves. The impression blocks together define the casting configuration,each impression block being carried in a pocket or nest defined by itsassociated holding block. Thus, the ejector die half and the cover diehalf is each comprised of an impression block and a holding block matedor nested together. To hold the two blocks of each die together theimpression block is usually friction fit into the pocket of its relatedholding block, i.e.,'the outer periphery of the impression block issubstantially equal to the periphery of the holding block's pocket. ingeneral practice, both blocks have been formed from steel. The system ofproviding an impression block-holding block structure for a die halfadmits of substantial economy because only the impression block need bereplaced, and not the entire die, when the cavity configuration becomesso eroded or washed out that an undesirable percentage of castings beingproduced is out of tolerance limits.

It has been found that the present steels known from which dies fordiecasting'type machines can be made do not themselves have a highenough melting point, nor are they suffieiently rugged, to withstand theeroding and washing characteristic and thermal and mechanical shockcharacteristics of the high melting point alloys so as to yield adesirable economic production life, To solve this problem it has beenproposed to provide impression blocks of refractory metals because thatgroup of metals is relatively resistant to thermal shock and cavityerosion at high diecasting temperatures. In the interest of economy, theholding blocks are still fabricated from high quality steels because ofthe high refractory metal cost. However, refractory metals areparticularly brittle at room temperature. Because the only knownpractical method of maintaining the impression block and holding blockin operable engagement is by friction fit techniques, it will be seenthat breakage of such impression blocks during the engaging anddisengaging of those blocks with their related holding block pockets isa definite problem and economic hazard. Also, when the outer peripheryof a refractory metal impression block is configured to conform to thesteel holding block pocket in a friction fit relationship at, forexample, room temperature, once the die assembly has risen to itsoperating temperature distinct expansion gaps or crevasses may occurbetween the periphery of the refractory metal impression block and theperiphery of the pocket in its associated steelholding block. Suchexpansion gaps may vary from thousandths of an inch to hundredths of aninch or more. This for the reason that the expansion coefficients of thenormal steels from which holding blocks are usually fabricated aresubstantially greater, for example, up to three or four times greater,than the expansion coefficients of the refractory metals from which theimpression blocks are fabricated. Such expansion crevasses or clearancesor gaps created between the impression block and associated holdingblock at high dieoperating temperatures may cause alignment or registrydifficulties for the cover and ejector impression blocks during repeatedopenings and closings of the die halves because of slippage or movementof one or both impression blocks within their holding block pockets,thereby rendering out of tolerance a substantial percentage of thecastings produced by the die assembly. The expansion gaps createdbetween the impression block and the holding block of the ejector diehalf at high die temperatures may, even be great enough so that theejector impression bloclc will actually be ejected from theejector-holding block by the ejector pins, after the die halves havebeen opened, during ejection of the formed casting. Also, during aproduction run the molten metal to be cast may squirt out between theinterface of the cover and ejector impression blocks and run into andsolidify in the expansion crevasses or gaps created, thereby preventingthe impression blocks from being removed from the holding block pocketsother than by breaking or otherwise cutting out the impression block.

Accordingly, it has been one objective of this invention to provide anexpansion gap compensating system associated with the impression blockand holding block of a die, that is, a

die half, that adequately retains and prevents movement ofthe impressionblock in the holding block pocket when the expansion coefficient of theimpression block material is substantially different from the expansioncoefficient of the holding block material.

It has been another objective of this invention to provide an expansiongap compensating system for a dies impression and holding blocks, whenthose blocks are made of materials having different expansioncoefficients, that is easily and readily adjustable during a casting runwhereby, as the die assembly rises to operating temperature from roomtemperature upon startup, as well as during the casting run, the systemis adjusted as required to compensate for expansion gaps or crevassesthat may tend to open, i.e., to compensate for the differentialexpansion of the materials, and as the die assembly declines fromoperating temperature the system is adjusted as required to compensatefor the contracting of those expansion gaps, i.e., to compensate for thedifferential contraction of the materials.

It has been still another objective of this invention to provide anexpansion gap system for a dies impression and hold ing blocks, whenthose blocks are made of materials having different expansioncoefficients, which precludes undesirable molten material that maysquirt out between the interface of the cover and ejector impressionblocks during a casting cycle from filling or running into any expansiongaps between sides of each die's impression and holding blocks adjacentthe face of each die caused by the difference in the blocks coefficientsof expansion.

It has been a further objective of this invention to provide anexpansion gap system for a dies impression and holding blocks, whenthose blocks are made of materials having different expansioncoefficients, that precludes movement of each impression block relativeto its associated holding block even during repeated adjustments to thesystem so as to permit opposed impression blocks of a die assembly to bemaintained in proper registry throughout a casting run.

These objectives have been attained in this invention by providing anexpansion gap compensating system for a die comprising, in combinationand in preferred embodiment form, (a) a holding block (fabricated of,for example, a steel) with a pocket defined therein, (b) an impressionblock (fabricated of, for example, a refractory metal) receivable withinthe pocket, the impression block having a substantially shorterperipheral length than the pocket so that when the two blocks areassembled a continuous fixed gap equal in length to at least one-halfthe peripheral length of the impression block is created between theimpression block and the holding block, (c) a chock positionable inwedging fashion within the fixed gap for maintaining the blocks togetheras a die, and (d) a key engageable with keyways in the bottom of thepocket and the impression block for establishing and maintainingaccurate relative position of the blocks one to the other. Each chock isprovided with adjustment means so that it can be tightened or loosenedwithin the fixed gap depending on the relative expansion or contractionof the blocks and the crevasses or expansion gaps between the blocksthat tend to be formed thereby. The expansion gap compensating system ofthis inventions preferred embodiment permits the impression block andthe holding block of a die, each of which is fabricated of a materialhaving a different expansion coefficient from the other, to be simplyand easily assembled and maintained together as a die in tight and safeoperating relation without damage to either, to be maintained in anexact centered or preset position relative one to the other even duringrepeated adjustments of the system, and to preclude undesirable moltenmaterial from filling any expansion gaps that occur between sides of theblocks adjacent the face of the die half, at all times throughout acasting run.

Other objectives and advantages of this invention will be more apparentfrom the following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is an axial cross-sectional view of a die assembly incorporatingthe expansion gap compensating system of this invention',

FIG. 2 is an elevational view, partially in cross section, taken alonglines 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along lines 3-3 of FIG.

FIG. 4 is a cross-sectional view of an alternate impression blockembodiment useful with the expansion gap compensation system;

FIG. 5 is a cross-sectional view similar to FIG. 3 of an alternativeembodiment ofa die assembly incorporating the expansion gap compensatingsystem of this invention;

FIG. 6 is a perspective view taken from the front of the alternativeembodiment of the die assemblys impression block; and

FIG. 7 is a perspective view taken from the rear of the alternativeembodiment of the die assemblys holding block with the back plateremoved; and

FIG. 8 is a cross-sectional view taken along lines 8-8 of FIG.

As illustrated in FIGS. l3, the principles of this invention areincorporated in a die assembly having an ejector or movable die 10 and acover or fixed die 11, the die halves being held in operationalengagement one with the other so as to define a die cavity 12 byapparatus, not shown, associated with any known type of diecastingmachine. The ejector die 10 is comprised of an ejector shoe or holdingblock 13 (fabricated of, for example, a tool steel) which establishes arectangular nest or pocket 14 in the front face of block 13. The pocket14 is sized to receive an ejector impression block 15 and an ejectorgate block 16 (both fabricated of, for example, a refractory metal) fromthe front face of holding block 13, and is defined by vertical sidewalls17 and a flat bottom 18 parallel to the front face of the holding block13. The bottom 18 of the pocket 14 provides structural support for theimpression block 15 when a charge of molten metal is received in the diecavity 12.

The impression block 15 and the gate block 16 are abutted end to end atjoint 19 in the pocket 14, and the free end of the gate block abuts gateend 21 of the pocket. It will be noted that the overall length L of theabutted impression block 15- -gate block 16 combination is substantiallyless than the length L of the pocket 14 so as to create an end gap 23 atone end between the impression block and the pocket end 22, see FIG. 2.Also, it will be noted that the widths W of the impression block 15 andgate block 16 are substantially less than the width W of the holdingblocks pocket 14 so as to create side gaps 24, 25 on both sides betweenthe sides of the impression block 15-gate block 16 combination and therelated pocket sides 17, see FIG. 2. Thus, the abutted impression block15- -gate block 16 combination has a shorter outer peripheral lengththan the peripheral length of the pocket 14, thereby creating the fixedgaps 23-25 that establish a single, continuous, fixed gap between theimpression block-gate block sides and three sides l7, l7 and 22 of thepockets four sides when those blocks are assembled together. It is to benoted that the continuous fixed gap 2325 is preferably equal in lengthto at least one-half the peripheral length of the impression blockl5-gate block 16 structure and, in the figures, is shown as being almostpercent the peripheral length of the gate block-impression blockstructure.

The ejector gate block 16 can move from one side to the other betweensides 17 of the pocket 14 because very precise positioning of this block16 within the pocket is not required, that is, if the gate block is offcenter by some hundredths of an inch this will not ordinarily adverselyaffect the quality of the castings produced. The ejector impressionblock 15, however, is positioned within the pocket 14 by a rectangularkey 27 extending lengthwise of the pocket, see FIG. 1. The key 27 isreceived in mating keyways 28, 29 sized to fit key 27, the keyways beingcut into the bottom 18 of the pocket 14 and into the bottom of theimpression block 15 respectively. The

key 27 is fixed to holding block 13 in keyway 24 by two bolts 31 theheads of which are recessed in the key. The key 27 serves to maintainthe impression block 15 in a precise, preset position or registry withinthe pocket 14 at all times, thereby preventing movement of theimpression block within the pocket relative to the holding block 13 inboth the north-south and east-west directions even when expansion gapson the order of thousandths of an inch or hundredths of an inch or moretend to open between the two blocks during use.

The ejector die is also illustrated as having two ejector pins 26 thatare selectively 'reciprocable into the die cavity 12 by ejectorapparatus, not shown, so as to eject castings formed in the cavity whenthe dies 10, 11 are opened.

In describing the cover die 11, elements of the cover die structure thatare similar to like parts of the ejector die 10 structure are given thesame reference number as used in describing the ejector die except thatthe letter a follows that number. The cover die 11 includes acover-holding block 1311 that defines a'cover nest or pocket 14a in thefront face of block 130, the pocket 14a and block 13a havingsubstantially the same peripheral dimensions and geometry as pocket 14and ejector-holding block 13. An impression block 1511 and gate block16a are abutted end to end at joint 19a in the pocket 14a in mirrorrelation to the impression block 15 and gate block 16 of the ejector die10, see FIG. 1. The cover impression 15a and gate 16a blocks are ofsubstantially the same outer peripheral dimensions and outer geometry asthe ejector impression 15 and gate 16 blocks. Thus, fixed gaps 23a-25asubstantially equal in dimension and configuration to fixed gaps 23-25of the ejector die 10 are also established for the cover die 11 betweensides 17al7a and ends 21a, 22a of the cover block's pocket 14a and thesides of the impression block 15a-gate block 160 combination. The covergate block 16a and holding block 13a are dissimilar from the ejectorgate 16 and holding blocks 13 in that they cooperate to define a gate ormolten metal inlet 33 for the die cavity 12. The inlet 33 receives theend 34 of a shot tube 35 passing through passageway 36 in-the holdingblock 13a and gate block 16a. A flange 37 integral with the shot tube 35is seated on the back of the holding block 13a to position the shot tuberelative to the gate 33. The shot tube 35 is part of a diecastingmachine, not completely shown.

The shot tube 35, being fixed, serves to maintain the gate block 16a inits preset position within pocket 14a. As with the ejector die 10, thecover impression block 15a is positioned within the pocket 14a by meansof a rectangular key 27a located in keyways 28a, 29a cut in the bottom18a of the pocket 14a and the bottom of the impression block 15a,respectively. The key 27a is fixed to holding block 13a in keyway 28a bybolts 31a in the same manner as for the ejector die 10.

As can be seen from the figures, when the two dies 10, 11 are closedinto cavity 12 forming relation for receiving a charge of molten metalthey meet at their front faces, that is, at die interface 41. Theimpression blocks 15, 15a cooperate to form the die cavity 12 which, inthe figures, is illustrated as that of a standard test bar. The gateblocks 16, 16a cooperate to establish the gate or metal inlet 33 for themolten metal, the gate terminating in an end feeder area 42 thatdistributes the molten metal into the die cavity 12. Guide pins 38 aremounted to. the cover-holdingblock 13a and are receivable in recesses 39formed in the ejector-holding block 13 for centering or locating theholding blocks 13, 13a in register when they are closed into operablediecasting position. When the dies 10, 11 are opened to eject a castingand then again closed to form cavity 12, keys 27, 27a act to ensure thatimpression block 15, 15a will be in registry by maintaining the presetposition of the impression blocks relative to their holding blocks 13,1311 even if expansion gaps or crevasses occur between the two blocksduring the casting operation. Movement of the ejector impression block15 relative to the cover'impression block 15a only a few thousandths ofan inch may, in complex casting configurations, so misalign those blocks15, 150 when they are closed together that castings produced from themwill be out of dimensional tolerance limits. Thus, keys 27, 27a play animportant part in maintaining the position of impression blocks 15, 15awithin their pockets 14, 14a and, in combination with guide pins 38 andrecesses 39, maintain the registry of the impression blocks duringrepeated openings and closings of the die assembly even when expansiongaps between impression and holding blocks occur.

Each impression block 15, 15a-gate block 16, 16a combination in eachholding blocks pocket 14, 14a, respectively, is maintained in thatpocket during use of the die assembly by restraining means or chocks43,4311 engageable with each die 10, 11 from the front face of that die.The chocks 43, 43a are preferably trapezodial or wedge shaped incross-sectional configuration, each chock having parallel top 44, 44aand bottom 45, 45a sides, a tapered side 46, 46a and a vertical side 47,470, the inwardly tapered sides meeting the top sides at an acute anglea, see FIG. 3. The chocks 43, 43a are positioned within and sized to fitin the fixed gaps 23-25,23a-25a created when the impression 15, 15a,gate 16, 16a, and holding 13, 13a blocks are assembled to substantiallyframe each block 15, 16 and 15a, 16a unit in its related pocket 14, 14a,see FIGS. 1 and 3. The impression blocks 15, 15a are provided withoutwardly tapered sides 48, 48a in an abotuse angle B, see FIG. 3. Thesum of the angles a and [3 equals Thus, the inwardly tapered sides 46,46a of the chocks 43, 43a are angled to cooperate with outwardly taperedsides 48, 48a of the impression 15, 15a and gate 16, 16a blocks so as torestrain those blocks in their respective pockets 14, 14a.

In essence, each impression block-gate block unit is restrained and,thereby, retained, in its pocket because of the wedging action of thechocks 43, 43a between the impression 15, 15a and gate 16, 16a blocksand the holding blocks 13, 13a.

It is to be noted that the chocks 43, 43a are ofa thickness Tsubstantially less than the depth D of the pockets 14, 14a so they canbe adjusted downward when required, as is more fully explainedhereinafter. The top side 44, 44a width of each chock 43, 43a ispreferably about equal to or a little less than the width at interface41 of the fixed gaps 23-25, 23a-25a that the chock is to serve when thedie is at room temperature. Thus, when the chocks 43, 4311 are initiallypositioned in a room temperature holding block 13, 13a during makeup ofthe die the top sides 44, 44a of the chocks are substantially parallelwith the front faces of the die halves 10, 11, see FIG. 3, andsubstantial clearance 49, 49a is established between the bottom side 45,45a of the chocks and the bottom 18, 18a of the pockets 14, 14a.

The chocks 43, 43a are maintained in operating position, and areadjustably positionable within fixed gaps 23-25, 23a- -25a during heatup, operation, and cool down of the die, by adjustment means in the formof threaded bolts 50, 50a spaced along'their length in mirror relationfor the ejector die 10 and the cover die 11; the bolts are available toan operator for adjustment from the front face of each die. The bolts50, 50a are engageable with the holding blocks 13, 13a by threads 52,52a that pass through, without threadedly engaging the chocks 43, 43a.Each bolthead 54, 54a cooperates with a recessed shoulder 53, 53a ineach chock 43, 43a for forcing the chock down toward the bottom of itsrelated pocket 14, 14a when the bolts 50, 50a are tightened into theholding blocks 13, 13a. Thus, by virtue of the wedging action performedby the chocks 43, 43a in the fixed gaps 23-25, 23a- 25a between thetapered sides of the impression-gate block units and the sides 17, 17a,22, 22a of the holding block pockets 14, 14a (the pressure of which canbe varied or adjusted by bolts 50, 50a) the impression blocks 15, 15aand gate blocks 16, 16a are easily and simply assembled and, thereafter,can be maintained together in tight and safe assembly during castingoperations even when expansion gaps tend to occur due to different blockmaterial expansion eoefficients and high temperatures. Therefore, notonly do the chocks 43, 43a maintain the impression blocks 15, 15a andgate blocks 16, 16a in nested position with the holding blocks 13, 130,but the geometry of the chocks in cooperation with the impression blocksand holding blocks also precludes undesirable molten metal or flashingfrom filling any expansion gaps between sides of the blocks adjacent thefaces of the blocks that might normally be caused by the difference inthe blocks coefficients of expansion because those expansion gaps arenever allowed to open through operation of adjustment means 50, 50a forthe restraining means 43, 430. Thus, no molten metal flashing runs intoexpansion gaps.

As is illustrated in FIGS. 1 and 3, the chock 43, 43a structure issubstantially the same for the chocks used with both the ejector die 10and the cover die 11, except that the depth of the working shoulder 53from the chock's top side 44 for the ejector die chocks 43 issubstantially deeper than that depth for the cover die chocks 43a. It ispreferred that shoulders 53a of the chocks 43a be recessed to a depthsubstantially less than the height of the boltheads 54a, and it ispreferred that the shoulders 53 of the chocks 43 be of substantiallygreater depth than the height of the boltheads 54. This for the reasonthat when the ejector l0 and cover 11 dies are mated in operatingrelation, and because of the symmetry and mirror relation of the dieassembly, the heads 54a of the cover chock bolts 5011 will be partiallyreceived within the deeper recesses of chock 43 where the bolts 50 arepositioned, see FIGS. 1 and 3. Such a relationship prevents molten metalfrom being forced or flashed into the area 55 between heads 54, 54a ofthe adjusting bolts during a casting cycle. If metal flashing got intothis area 55 it could fuse the boltheads 54, 54a together and hinderseparation of the die halves 10, 11. If, for example, Allen head boltsare used and metal fills the wrench recess on the Allen head, removal ofthe adjusting bolts 50, 50a from the chocks 43, 43a and holding blocks13, 13a also would be extremely difficult.

The chock 43, 43a structure of this invention admits of a method of usewhich is unique and novel in that it easily and simply permits theimpression block 15, 15a to be changed with its related holding block13, 13a. That is, the necessity for a tight friction fit between theimpression block 15, 15a and holding block 13, 130 has been eliminatedby the method and structure of this invention, thereby lessening thepractical problems that obtain when handling, for example, refractorymetal impression blocks which are relatively brittle at roomtemperature. In use, the impression block 15, 15a and gate block 16, 16aare placed in the holding blocks pocket 14, 140 from the front face ofthe die 10, 11, those blocks and pocket being formed so as to createfixed gaps 23-25, 2311-250 between the sides of the impression block 15,15a and the sides 17, 17a, 22, 22a of the holding block pocket 14, 14a.The key 27, 27a is positioned in the keyways 28-29, 28a- 29a provided inthe bottom 18, 18a of the pocket 14, 14a and the bottom of theimpression block 15, 15a, thereby centering the impression block in theholding blocks pocket. Because the impression block-gate block unit isformed with a peripheral length less than the peripheral length of theholding block's pocket 14, 140 the impression block 15, 15a can beeasily and gently set down into the holding block's pocket. This is ofsubstantial advantage for refractory metal impression blocks in that itlessens the chance of cracking through mishandling. Subsequently, thechocks 43, 43a are positioned within those gaps 23-25, 23a-25a from thefront face of the die 10, 11 in a wedging fashion so as to maintain theimpression block 15, 15a immobile relative to the holding block 13, 13a.The chocks 43, 43a are tightened in position from the front face of thedie 10, 11 by tightening the bolts 50, 50a and, thus, the impressionblock 15, 15a is tightly and safely restrained in operating assemblywith the holding block 13, 1311. Even if the chocks 43, 43:: aretightened with unequal pressure on either side of the impression block15, 15a, those blocks still maintain their preselected alignment becauseof the key 27, 27a and keyways 28-29, 28a-29a. Such a method andstructure has been found to substantially reduce the amount oftimerequired by an operator to change imprcs sion blocks in a holding block.

The problems that occur when using a refractory metal im pression block15, 15a with a normal-grade steel-holding block 13, 13a arise because ofthe difference in expansion coefficients between these materials, asheretofore explained. The refractory metals have a much lowercoefficient ofexpansion than do steels, for example, a refractory metalalloy may have a coefficient of expansion only one-half to one-thirdthat of a good grade steel. Hence, in the prior art, even though animpression block may have a tight friction fit with the holding blockspocket when it is first assembled in operating position with that pocketat room temperature, as the die assembly heats up to operatingtemperature the sides of the pocket of the steel-holding block tend toexpand away from the sides of the refractory metal impression block.That is, the impression block does not expand as much as the holdingblock to maintain the tight friction fit; therefore, expansion gaps orcrevasses on the order of thousandths of an inch or hundredths of aninch or more are formed during high-temperature operation between theimpression block and the sides of the holding blocks pocket when theprior art method of holding the two blocks in operating engagement isused. In solving these problem, the chock 43, 43a structure ofthisinvention is utilized by the method steps of periodically tightening thechocks 43, 43a from the front face of the die 10, 11 as the die heats upto operating temperature by means of adjusting bolts 50, 50a to take upany expansion gaps or crevasses created, thereby maintaining theimpression block in tight and safe operating assembly with the holdingblock 13, 13a and preventing expansion gaps from opening in the firstinstance. This step drives the wedge-shaped chocks 43, 43a deeper intothe fixed gap 23-25, 230-2511, but the original clearance 49, 49abetween the bottom 18, 18a of the pockets 14, 14a and the bottom 45, 45aof the chocks permits such limited movement to be achieved. Suchtightening of bolts 50, 50a also can be performed by an operator fromthe readily accessible front face of each die 10, 11 when the die halvesare momentarily parted for ejecting a casting at the end of one castingcycle during a casting run, that is, the die does not have to bedismounted from the casting machine or disassembled to make the requiredadjustments. After a casting run has been concluded, and as the dieassembly is cooling down to room temperature for changing impressionblocks 15, 1511 (thereby causing the expansion gap formed on heat up tocontract), the chocks 43, 43a are periodically loosened by unscrewingbolts 50. This prevents any buildup of compressive forces between theholding block 13, 13a and the impression block 15, 15a that may causethe brittle impression block to crack. Thus, this method easily andsimply permits takeup of any expansion gap or crevasse created duringheat up and operation of the die assembly, thereby maintaining theimpression block in tight operating assembly and registry with theholding block during a casting run without the necessity of periodicallydismounting or disassembling the die, and thereby preventing expansiongaps from forming which precludes molten metal flashing from flowinginto such gaps. Also, this method easily and simply permits thatexpansion gap to be recreated or Opened as the die assembly is cooleddown and the impression 15, 15a and holding 13, 13a blocks contract backto normal room temperature configuration, thereby preventing cracking ofthe impression block on cooling that may occur if intolerable pressuresare created on the brittle refractory metal impression blocks.

When the impression block 15, 15a is fabricated of, for example, arefractory metal and the holding block 13, 13a is fabricated of, forexample, a tool steel it is preferred that the chocks 43, 4311 befabricated of that tool steel and the key 27, 27a be fabricated of thatrefractory metal. 1n the case of the chocks 43, 43a, they must usuallybe made of steel so they can withstand the stresses placed on them bytightening of the bolts 50, 50a. ln the case of the key 27, 270, it isdesirably fabricated of the same material as the impression block 15,15:: so that no slippage or gaps occur between the key and its relatedimpression blocks because both expand and contract at equal rates. Evenif small gaps occur between the key 27,

' 27a and the holding block keyway 28, 28a, because the key is bolted tothe holding block 13, 13a such gaps cannot adversely affect the centeredposition of the impression and holding blocks. Thus, in the veryimportant phase of registry or block alignment it is by means of the key27, 27a, keyways 2829, 28a-29, and bolts 31, 31a fixing the keys to theholding blocks 13, 13a that the impression blocks 15, a are maintainedin a centered position relative to the holding blocks pockets 14, 14a.Over tightening on one of the chocks 43, 43a by an operator relative toanother of the chocks may inadvertently move the impression block 15,15a off center a substantial number of thousandths of an inch withoutthe keykeyway structure, however, this structure prevents such ahappenstance from occurring.

The impression blocks 15, 15a illustrated in FIGS. 1-3 have been shownas defining a single die cavity. However, an

alternative embodiment for the impression block, as illustrated in FIG.4, is one having one-half 61 of a first die cavity on its front face 62and one-half 63 of a second die cavity on its back face 64. Thisalternative embodiment can be flipped over in a holding blocks pocketwhen a casting configuration change is required. Such an impressionblock admits of substantial economy particularly when that block isformed of a high-cost material such as a refractory metal in that twocastings, instead of just one, can be cast from it. As can be seen fromFIG. 4, the cross-sectional angle [3 defined by each face 62, 64 withthe tapered sides 65 of the impression block is an obtuse angle, therebymaking such a block configuration useful with the expansion gap systemof this invention.

An alternativeembodiment of a die assembly incorporating the expansiongap compensating system of this invention is illustrated in FIGS. 5-8.The alternative embodiment of a die half 70 basically differs from theembodiment illustrated in FIGS. 1-3 in that (a) impression block 71 isinserted from the rear of holding block 72 instead of from the face ofthe holding block as with the preferred embodiment, and (b) theimpression block 71 is automatically adjustable during use of the dieassembly's alternative embodiment to compensate for expansion gaps thattend to open between sides of related impression and holding blocks attheir face as the die assembly is heated up to operating temperature, aswell as to compensate for contraction of the gaps as the die assemblycools after a casting run.

As illustrated in FIGS. 57 each die half 70 of the alternativeembodiment is comprised of a holding block 72, an impression block 71,and a rear plate 73. The casting cavity 69 illustrated is that same typeof test bar as illustrated in the preferred embodiment of FIGS. 1-3.

The holding block 72 is provided with a specially configured pocket 74that extends completely through the holding block. The pocket 74 isconfigured to provide a seat 75 or recess in the rear surface 76 of theholding block 72, the seat being defined by'verticalsidewalls 77perpendicular to the rear surface and a bottom wall 78 substantiallyparallel to the rear surface of the holding block. The holding blockspocket 74 is further defined by angulated cam walls 79 which extend fromthe bottom wall 78 of the seat 75 to the face 81 of the holding block72. The angulated walls 79 define a hole more or less in the shape ofa'truncated tetrahedron, the minor face of the tetrahedron being at theface 81 of the holding block and the major face of the tetrahedron beingat the bottom wall 78 of the seat 75 in the holding block 72, that is,the periphery of the hole at the face of the holding block issubstantially less than the periphery of the hole at the bottom wall ofthe seat in the holding block. This configuration, i.e., the cam walls79, provides wedgelike surfaces for that portion of the pocket 74adjacent the face 81 of the holding block 72.

The impression block 71 is especially configured to cooperate with thepocket 74 in the holding block 72. The impression block 71 is comprisedof a base 84 which is of a width A and of a length B substantially lessthan the width A and length B ofthe seat 75 in the holding block 72, seeFIG. 8. This configuration allows fixed gaps 85 to be establishedbetween the sides 86 and ends 87 of the base relative to the sidewalls77 and bottom 78 of the seat 75 when the impression block 71 isoperationally engaged with the holding block 72, see FIGS. 5 and 8.Further, the depth C of the impression blocks base 84 is substantiallyless than the depth C of the seat 75 in the holding block 72.

The impression blocks base 84 is formed integral with a truncatedtetrahedron 91 which presents a face 92 having an outer periphery 93that is substantially identical with the periphery 94 of the holedefined by cam walls 79 at the face 81 of the holding block 72 at roomtemperature. The truncated tetrahedron 91 is of the same cross-sectionalconfiguration as is the hole defined by cam walls 79, but the depth D ofthe truncated tetrahedron is substantially greater than the depth D' ofthe hole defined by cam walls 79 in the holding block 72. Thus, when theimpression block 71 and holding block 72 are assembled, a fixed gap 96between the bottom wall 78 of holding block's seat 75 and the ledge 97of the impression blocks base 84 is also created. Further, it will benoted that the overall depth (C +D) of the impression block 71 is equalto the overall depth (c+D) of the pocket 74 in holding block 72.

Of course, the impression block 71 is made from a material having adifferent expansion coefficient than that of holding block 72, as in thecase of the preferred embodiment, and it is preferred that theimpression block be configured during manufacture so that, whenassembled with the holding block at room temperature, the face 92 of theimpression block is substantially flush or in the same horizontal planewith the face 81 of the holding block.

The impression block 71 is held in operative engagement with the holdingblock 72 by means of the backplate 73 which is fixed to the holdingblock by means of threaded bolts 102 (shown only in FIG. 5). Thebackplate 73 cooperates with the impression block 71 to maintain 'samein fixed or wedged engagement with the cam sides 79 of the holdingblocks hole pocket 74 at room temperature. The backplate 73 ispreferably made of the same material as the holding block 72.

The backplate 73 is provided with a key 103 which cooperates with akeyway 104 in the impression block 71 to maintain same in exact positionor registry during use of the die assembly. The key 103 is comprised ofan elongated bar that is fixed by bolts 105 to the backplate 73, and thekey is made of the same material as the impression block 71.

Because of the expansion gap phenomena explained in connection with thepreferred embodiment of this invention, as the die assembly illustratedin FIGS. 5-8 is heated up during use expansion gaps or crevices willoccur between the cam sidewalls 79 of the holding block and the camsidewalls 106 of the impression block 71. So that such expansion gaps orcrevices are not open at the face 92, 81 of the die half 70, restrainingmeans in the form of a series of threaded bolts 108 each with aheavy-spring washer 109 are-spaced around the periphery of the pocket 74at face 81 of the holding block 72 to assure that such expansion gaps donot form. One of the holding blocks 72 is provided with a series ofrecesses 110 of a depth substantially greater than the depth of theboltheads 111. Those recesses 110 are aligned relative to the peripheryof pocket 74 so that a further hole 112 may be bored completely throughledge section 114 of the holding block 72 in alignment with. a hole 113through base section 84 of the impression block 71, the ledge section114 and base section 84 overlapping as seen in cross section in FIG. 5.The diameter of holes 112, 113 is such that bolts 108 are not threadedlyengaged therewith. The bolts 108 are inserted through the holes 112, 113in the impression block 71 and holding block 72 and are each providedwith heavy spring or disc washer 109 interposed between nut 116 and therear 76 of the impression block. Seats 117 are provided in the baseplate73 to receive the nutted end of the bolts 112. The springs 109 cooperatewith the bolts 108 to continually pressure the cam sides 106 of theimpression block 71 against, and to insure that the cam sides of theimpression block are held in engagement with, the

cam sidewalls 79 of the holding blocks pocket 74 during a casting run,even when expansion gaps or crevices tend to occur. This prevents anyexpansion gaps from occurring at the face 92, 81 of the die half 70 inwhich molten metal may freeze, and also holds the impression block 71and holding block 72 in operable engagement once the temperature of thedie half has increased to a point where the baseplate 73 no longerserves that purpose.

The holding block 72a of the other mold half 70a is provided with boltholes 110a of a depth substantially less than the height ofthe boltheadsIlla, and the holes 110a are positioned in mirror relation to theboltholes H of the die half 70. Thus, when the two die halves 70, 70aare in operable en gagement (see FIG. to define the casting cavity 69,boltheads 111a are received in recesses 110 in the holding block 70 soas to essentially seal off that space 121 between boltheads ll], 111aand prevent molten metal from freezing the bolts in position.

Although I have described the preferred embodiment of my invention incomplete detail it will be understood by those skilled in the art thatvariations and modifications may be established in the expansion gapsystem structure and method of this invention as described hereinwithout departing from the spirit or scope of the appended claims. Forexample, even though the inventive concept of this application has beendescribed primarily with reference to the art of diecasting, it will beunderstood that the inventive principles are also applicable topermanent molding, centrifugal molding, gravity molding and otherrelated areas where a die is utilized comprised of a holding block andan impression block wherein the expansion coefficients of those blockmaterials cause problem (s) such as are discussed above. Accordingly,having fully disclosed the preferred embodiment of my invention, what Idesire to claim and protect by Letters Patent is:

l. A method of compensating for expansion gaps in a die wherein each diehalfis made up ofa holding block and an impression block, and whereinthe coefficient of expansion of said holding block is greater than thecoefficient of expansion of said impression block, comprising the stepsof providing a pocket in said holding block providing said impressionblock with an outer periphery configured such that said impression blockcan be established in nested position within said holding block'spocket, said impression block thereafter being nested in said holdingblocks pocket, providing restraining means associated with saidimpression and holding blocks that maintains said impression block innested position with said holding block, and that precludes undesirablemolten material from filling any expansion gaps between sides of saidblocks adjacent the face of said die half that might normally be causedby the difference in said blocks coefficients of expansion, as thetemperature of said die half rises during use thereof,

charging molten material into the cavity of said die half therebyincreasing the temperature of said die half and promoting differentialexpansion between said impression block and said holding block, and

adjusting said restraining means to compensate for the differentialexpansion of said impression block and said holding block as thetemperature of said die half rises, thereby alleviating the formation ofexpansion gaps between the sides of said impression and holding blocksadjacent the face ofsaid die halfduring use thereof.

2. A method as set forth in claim 1 including the further steps ofreturning the temperature of said die toward ambient temperature, and

adjusting said restraining means to compensate for the differentialcontraction of said impression block and said holding block as thetemperature of said die half decreases, thereby permitting thecontraction of the expansion gap formed between the sides of saidimpression and holding blocks as the temperature of said die half wasrising without subjecting said impression block to undesirablecompressive forces.

3. A method as set forth in claim 2 including the further step ofproviding registration means associated with said holding and impressionblocks for maintaining desired registry of each of said die halfsimpression blocks to each other during adjusting of said restrainingmeans.

4. A method as set forth in claim 3 wherein said impression block isprovided with an outer periphery substantially less than the peripheryof said pocket, and said impression block is positioned in said pocketso a preformed gap is created between the sides of said impression blockand said holding block, and including the further step of inserting saidrestraining means within said preformed gap.

5. A method as set forth in claim 3 wherein the step of providingregistering means includes keying said impression block to said holdingblock.

6. A method as set forth in claim 4 wherein said restraining means is achock and said chock is inserted in wedging fashion within said gap.

7. A method as set forth in claim 6 wherein said chock is inserted untilthe top side of said chock is substantially flush with the front face ofsaid impression block at ambient temperature, said chock being so sizedthat a clearance is thereby established between the bottom of said chockand the bottom of said pocket at ambient temperature.

8. A method as set forth in claim 7 wherein said chock is adjusted bythe manual tightening and loosening of bolts interconnecting said chockand said holding block.

9. A method as set forth in claim 8 wherein said impression block ispositioned, said chock is'inserted, and said bolts are adjusted all fromthe front face of said die half.

10. An expansion gap compensating system for a die assembly having twocomplimentary die halves, at least one die half comprising, incombination,

a holding block with a pocket defined therein,

an impression block established in nested position within said holdingblocks pocket, the impression block material having a lesser expansioncoefficient than the holding block material,

restraining means associated with said impression and holding blocks,said restraining means maintaining said impression block in nestedposition with said holding block, and said restraining means cooperatingwith said blocks to preclude undesirable molten material from fillingany expansion gap between the sides of said blocks adjacent the face ofsaid die half that might normally be caused by the difference in saidblocks coefficients of expansion, as the temperature of said die halfrises during use thereof, and

adjusting means associated with said impression and holding blocks foradjusting said restraining means as required to compensate for thedifferential expansion of said impression and holding blocks as the diehalfs temperature rises during use, thereby alleviating the formation ofan expansion gap between the sides of said impression and holding blocksadjacent the face of said die half during the use thereof.

11. An expansion gap compensating system as set forth in claim 10wherein said adjusting means also includes means adapted for adjustingsaid restraining means as required to compensate for the differentialcontraction of said impression and holding blocks as the temperature ofsaid die half decreases, thereby permitting the contraction of theexpansion gap formed between the sides of said impression and holdingblock as the temperature of said die half was rising without subjectingsaid impression block to undesirable compressive forces.

12. An expansion gap system as set forth in claim 11 includingregistration means associated with said impression and holding blocksfor maintaining desired registry of said impression block with acooperating impression block of another die half during use of saidadjustment means.

13. An expansion gap system as set forth in claim 12 wherein saidregistration means comprises key means.

14. An expansion gap compensating system as set forth in claim 12wherein the periphery of said impression block is substantially lessthan the periphery of said holding blocks pocket, said dissimilarperipheries resulting in a preformed gap between the sides of saidblocks equal to at least about one-half the peripheral length of saidimpression block being disposed between the sides of said impressionblock and said holding block's pocket, and wherein said restrainingmeans is positioned within said preformed gap.

15. An expansion gap compensating system as set forth in claim 14wherein said restraining means comprises a chock positioned within saidfixed gap 16. An expansion gap compensating system as set forth in claim15 wherein said chock is wedge shaped in cross-sectional configuration,and wherein said chock is fabricated of the same material as saidholding block.

17. An expansion gap compensating system as set forth in claim 15wherein the thickness of said chock is substantially less than the depthof said fixed gap so that a clearance is established between the bottomof said chock and the bottom of said pocket when said chock ispositioned within said gap at ambient temperature, and wherein the topside of said chock is substantially flush with the front face of saidimpression block when said chock is positioned within said gap atambient temperature.

18. An expansion gap compensating system as set forth in claim 14wherein said registration means comprises key means engageable with saidholding block and said impression block.

19. An expansion gap compensating system as set forth in claim 18wherein said key means includes a key, and

a keyway in at least one of said impression blocks and said pocket.

20. An expansion gap compensating system as set forth in claim 19wherein said key is fixed to said holding block, a keyway is at least insaid impression block, and said key is of the same material as saidimpression block.

21. An expansion gap compensating system as set forth in claim 17wherein said adjusting means includes a series of bolts interconnectingsaid chock and said holding block, said chock and said bolts beingaccessible from the front face of said die half.

22. An expansion gap compensating system as set forth in claim 16wherein said impression block and chock are configured so that an obtuseangle is formed between the front face and side of said impression blockand a mating acute angle is formed between the top and side of saidchock, said angles totaling about 23. An expansion gap compensatingsystem for a die assembly having two die halves comprising, incombination,

a first and a second holding block with pockets defined therein,

a first and a second impression block each receivable within one of saidpockets, the impression blocks material having a lesser expansioncoefficient than the holding blocks material and said impression blockseach having a substantially shorter peripherallength than its relatedpocket so that a fixed gap is created for each pair of blocks,

a chock positionable within each of said gaps, said gaps being in mirrorrelation one to the other when said die halves are positioned togetherin operable die assembly,

a first series of bolts adjustably interconnecting a first chock andsaid first holding block from the front face of said first die half, thefirst boltheads being substantially recessed below the top side of thefirst said chock, and

a second series of bolts adjustably interconnecting a second said chockand said second holding block, the second boltheads extendingsubstantially above the top side of the second said chock and beinggositioned in mirror relation to said first bolts, and the eads of saidsecond bolts being received in the deeper recesses formed for said firstbolts after said die halves are positioned in operable die assembly, t

both said series of bolts adapted to be turned to periodically adjustthe position of the respective chocks within the respective fixed gapsto compensate for widening or narrowing of said fixed gap as the dietemperature increases and decreases, respectively, from and to ambienttemperature during use.

1. A method of compensating for expansion gaps in a die wherein each diehalf is made up of a holding block and an impression block, and whereinthe coefficient of expansion of said holding block is greater than thecoefficient of expansion of said impression block, comprising the stepsof providing a pocket in said holding block providing said impressionblock with an outer periphery configured such that said impression blockcan be established in nested position within said holding block''spocket, said impression block thereafter being nested in said holdingblock''s pocket, providing restraining means associated with saidimpression and holding blocks that maintains said impression block innested position with said holding block, and that precludes undesirablemolten material from filling any expansion gaps between sides of saidblocks adjacent the face of said die half that might normally be causedby the difference in said blocks'' coefficients of expansion, as thetemperature of said die half rises during use thereof, charging moltenmaterial into the cavity of said die half thereby increasing thetemperature of said die half and promoting differential expansionbetween said impression block and said holding block, and adjusting saidrestraining means to compensate for the differential expansion of saidimpression block and said holding block as the temperature of said diehalf rises, thereby alleviating the formation of expansion gaps betweenthe sides of said impression and holding blocks adjacent the face ofsaid die half during use thereof.
 2. A method as set forth in claim 1including the further steps of returning the temperature of said dietoward ambient temperature, and adjusting said restraining means tocompensate for the differential contraction of said impression block andsaid holding block as the temperature of said die half decreases,thereby permitting the contraction of the expansion gap formed betweenthe sides of said impression and holding blocks as the temperature ofsaid die half was rising without subjecting said impression block toundesirable compressive forces.
 3. A method as set forth in claim 2including the further step of providing registration means associatedwith said holding and impression blocks for maintaining desired registryof each of said die half''s impression blocks to each other duringadjusting of said restraining means.
 4. A method as set forth in claim 3wherein said impression block is provided with an outer peripherysubstantially less than the periphery of said pocket, and saidimpression block is positioned in said pocket so a preformed gap iscreated between the sides of said impression block and said holdingblock, and including the further step of inserting said restrainingmeans within said preformed gap.
 5. A method as set forth in claim 3wherein the step of providing registering means includes keying saidimpression block to said holding block.
 6. A method as set forth inclaim 4 wherein said restraining means is a chock and said chock isinserted in wedging fashion within said gap.
 7. A method as set forth inclaim 6 wherein said chock is inserted until the top side of said chockis substantially flush with the front face of said impression block atambient temperature, said Chock being so sized that a clearance isthereby established between the bottom of said chock and the bottom ofsaid pocket at ambient temperature.
 8. A method as set forth in claim 7wherein said chock is adjusted by the manual tightening and loosening ofbolts interconnecting said chock and said holding block.
 9. A method asset forth in claim 8 wherein said impression block is positioned, saidchock is inserted, and said bolts are adjusted all from the front faceof said die half.
 10. An expansion gap compensating system for a dieassembly having two complimentary die halves, at least one die halfcomprising, in combination, a holding block with a pocket definedtherein, an impression block established in nested position within saidholding block''s pocket, the impression block material having a lesserexpansion coefficient than the holding block material, restraining meansassociated with said impression and holding blocks, said restrainingmeans maintaining said impression block in nested position with saidholding block, and said restraining means cooperating with said blocksto preclude undesirable molten material from filling any expansion gapbetween the sides of said blocks adjacent the face of said die half thatmight normally be caused by the difference in said blocks'' coefficientsof expansion, as the temperature of said die half rises during usethereof, and adjusting means associated with said impression and holdingblocks for adjusting said restraining means as required to compensatefor the differential expansion of said impression and holding blocks asthe die half''s temperature rises during use, thereby alleviating theformation of an expansion gap between the sides of said impression andholding blocks adjacent the face of said die half during the usethereof.
 11. An expansion gap compensating system as set forth in claim10 wherein said adjusting means also includes means adapted foradjusting said restraining means as required to compensate for thedifferential contraction of said impression and holding blocks as thetemperature of said die half decreases, thereby permitting thecontraction of the expansion gap formed between the sides of saidimpression and holding block as the temperature of said die half wasrising without subjecting said impression block to undesirablecompressive forces.
 12. An expansion gap system as set forth in claim 11including registration means associated with said impression and holdingblocks for maintaining desired registry of said impression block with acooperating impression block of another die half during use of saidadjustment means.
 13. An expansion gap system as set forth in claim 12wherein said registration means comprises key means.
 14. An expansiongap compensating system as set forth in claim 12 wherein the peripheryof said impression block is substantially less than the periphery ofsaid holding block''s pocket, said dissimilar peripheries resulting in apreformed gap between the sides of said blocks equal to at least aboutone-half the peripheral length of said impression block being disposedbetween the sides of said impression block and said holding block''spocket, and wherein said restraining means is positioned within saidpreformed gap.
 15. An expansion gap compensating system as set forth inclaim 14 wherein said restraining means comprises a chock positionedwithin said fixed gap.
 16. An expansion gap compensating system as setforth in claim 15 wherein said chock is wedge shaped in cross-sectionalconfiguration, and wherein said chock is fabricated of the same materialas said holding block.
 17. An expansion gap compensating system as setforth in claim 15 wherein the thickness of said chock is substantiallyless than the depth of said fixed gap so that a clearance is establishedbetween the bottom of said chock and the bottom of said pocket when saidchock is positioned within said gap at ambient temperature, and whereiNthe top side of said chock is substantially flush with the front face ofsaid impression block when said chock is positioned within said gap atambient temperature.
 18. An expansion gap compensating system as setforth in claim 14 wherein said registration means comprises key meansengageable with said holding block and said impression block.
 19. Anexpansion gap compensating system as set forth in claim 18 wherein saidkey means includes a key, and a keyway in at least one of saidimpression blocks and said pocket.
 20. An expansion gap compensatingsystem as set forth in claim 19 wherein said key is fixed to saidholding block, a keyway is at least in said impression block, and saidkey is of the same material as said impression block.
 21. An expansiongap compensating system as set forth in claim 17 wherein said adjustingmeans includes a series of bolts interconnecting said chock and saidholding block, said chock and said bolts being accessible from the frontface of said die half.
 22. An expansion gap compensating system as setforth in claim 16 wherein said impression block and chock are configuredso that an obtuse angle is formed between the front face and side ofsaid impression block and a mating acute angle is formed between the topand side of said chock, said angles totaling about 180*.
 23. Anexpansion gap compensating system for a die assembly having two diehalves comprising, in combination, a first and a second holding blockwith pockets defined therein, a first and a second impression block eachreceivable within one of said pockets, the impression blocks'' materialhaving a lesser expansion coefficient than the holding blocks'' materialand said impression blocks each having a substantially shorterperipheral length than its related pocket so that a fixed gap is createdfor each pair of blocks, a chock positionable within each of said gaps,said gaps being in mirror relation one to the other when said die halvesare positioned together in operable die assembly, a first series ofbolts adjustably interconnecting a first chock and said first holdingblock from the front face of said first die half, the first boltheadsbeing substantially recessed below the top side of the first said chock,and a second series of bolts adjustably interconnecting a second saidchock and said second holding block, the second boltheads extendingsubstantially above the top side of the second said chock and beingpositioned in mirror relation to said first bolts, and the heads of saidsecond bolts being received in the deeper recesses formed for said firstbolts after said die halves are positioned in operable die assembly,both said series of bolts adapted to be turned to periodically adjustthe position of the respective chocks within the respective fixed gapsto compensate for widening or narrowing of said fixed gap as the dietemperature increases and decreases, respectively, from and to ambienttemperature during use.